I think you might just be a genius. I switch my immersion spur off and pressed this reset switch and (whilst only early days) it seems to have kicked the boiler on for the water! Will see how it goes and let you all know if this fixed it.
Side note, if this little reset button has cost me a ton of electricity for 2 years I'm gonna be annoyed with myself
Fingers crossed, but turning the spur off should have been all that was required.
My current customer complained about their electricity costs a year ago. I asked why the megaflow element was on. I turned it off and their bill dropped.